Process for eluting pentavalent vanadium values from ion exchange resins



United States Patent PROCESS FOR ELUTING PENTAVALENT VANA- DIUM VALUESFROM ION EXCHANGE-RESINS Daniel C. McLean, Springdale, Conn., as sig'norto American Cyanamid Company, New York, N.Y., a corporation of Maine NoDrawing. Application August 9, 1955 Serial No. 521,401

This invention relates to an improved method of eluting vanadiumadsorbed on anion exchange resins.

While the adsorption of vanadium by anion exchange.

resins was not a commercially practical'proc'ess until the developmentof the process described and claimed in my copending application, SerialNo. 527,400, filed August 9, 1953, in which the adsorption of thevanadium from feed liquor containing it in high concentration waseffected at a temperature below that at which insoluble polyvanadateprecipitation took place and preferably at temperatures not exceeding 40C. followed in series by further resin beds maintained at hightemperatures, attempts were made to elute vanadium adsorbed on anionexchange resins. One of these attempts involved the use of an aqueoussulfurous acid solution which reduced the pentavalent vanadium adsorbedon the resin to vanadyl sulfate which was soluble in the eluate. Thisproposed method of elution, however, ran into serious operationalproblems. The reaction taking place during elution by which thepentavalent vanadium is reduced to the tetravalent formconsumedsulfurous acid with the result that the pH of the solution rose, andusually hydrolysis set in, resulting in the precipitation of vanadiumcompounds in the resin in a form in which they could not readily beremoved. It was only possible to avoid this difficulty by the use of avery large volume of the eluting liquid. This is feasible in thelaboratory but is impractical in commercial use because the extremelydilute eluate obtained contains a very large amount of S0 which has tobe destroyed by oxidation and renders the cost of operation prohibitive.7

According to the present invention the elution with sulfurous acid iseffected without undesirable precipitation. I have found that thisresult may be obtained by greatly increasing the rate at which thesulfurous acid solution is circulated through the resin containing theadsorbed vanadium, until such time as the vanadium content of the resinis markedly lowered, at which point a slower elution does not result inprecipitation.

The rapid elution which is kept at a rate above that causingprecipitation, and in practical operation will preferably result in acontact time of the order of a minute or even less, does not produce adilute eluate because recycling is used until the vanadium content inthe eluate has built up to the point at which S0 losses in the finalrecovery are not serious. Preferably the elution is continued until thevanadium content in the eluate reaches a value up to 90 grams per liter(which throughout the specification will be abbreviated as g./l.). Inrecycling care should be taken to keep the pH of the eluting solutionfrom rising too high. This can be effected very easily by the additionof small amounts of sulfuric acid. The pH should be kept well below 2,but if the pH falls too low, that is below-about 1.3, the solubility ofthe S0 becomes too low and during recycling, its evolution as a gasintroduces an operating nuisance, requiring scrubbing facilities and thelike.

When a resin bed or column with a heavy vanadium loading is first elutedby rapid recycling of the eluant, if necessary with pH adjustment, ahigh concentration of vanadium in the eluate is obtained for thevanadium adsorbed on the outer surfaces of the resin beads elutescomparatively very rapidly whereas the vanadium which is more deeplyimbedded comes out quite slowly. The strong eluate containing highvanadium content is sent to vanadium recovery where the vanadium isoxidized to the point where it precipitates as a polyvanadate referredto in the art as red cake. S0 losses per unit of vanadium recovered arecomparatively small. As the vanadium content of the resin decreases,elution can be slower without hydrolysis and is carried out until thevanadium content of the resin has been brought down to the desiredminimum. In these latter stages in the interest of output there shouldbe sufiicient volume of sulfurous acid solution so that it is present inlarge excess; or, to put it in other terms, an eluate is produced whichhas a relatively low vanadium content. In the case of the last of theeluate this may be as little as 5% or less ofv the vanadium content ofthe earlier eluates. To oxidize such a dilute solution in order toprecipitate the vanadium as polyvanadate would result in serious lossesof S0 and excessive consumption of oxidizing agent. This disadvantage issmaller although not quite so serious than that encountered when verylarge volumes of eluant are used from the'beginning as was necessary inthe former process. Therefore, it is preferable to use the later eluateswith small vanadium contents as part or all of the eluant used with thenext batch of vanadium-loaded resin. Of course, fortification withadditional S0 and adjustment of pH should first take place. In this waythe S0 content of the later eluates is eflectively utilized.

The invention will be described in greater detail in conjunction withthe following specific examples.

, Example 1 A strong base anion resin of the quaternary ammoniumpolystyrene-divinyl benzene type described in US. Patent No. 2,591,573and sold by Rohm and Haas under the designation XE-123 having a resinloading in g./l. of 232 V 0 and 8 Fe was eluated with 2.8 column volumesof an eluant of pH 1.0 containing 60 g./1. S0 The eluant was passedthrough the resin bed as fast as it would flow with an average retentiontime of approximately 1 minute. The eluant was recycled with adjustmentof pH until the odor of S0 was no longer noticeable. The eluatecontained in g./l. 88.6 V 0 and 3.65 Fe. This eluate was oxidized withsodium chlorate and adjusted with alkali until the vanadium precipitatedas red cake.

Meanwhile a second 2.8 column volumes of eluant was recycled through theresin, the pH being maintianed at 0.75. The contact time remained about1 minute. Recycling was continued as beforeuntil the odor of was nolonger noticeable. An eluate was produced containing in g./l; 26.6 V 0and 0.4 Fe. eluate was likewise oxidized as described above toprecipitate red cake.

A third 2.8 column volumes of eluant was recycled at a slower rate withabout a 10 minute contact time.

7 The pH was maintained at 1.5. An eluate was produced containing 1.2g./l. V 0 and negligible Fe. The third elution exhausted substantiallyall of the vanadium from the resin which was then used as an adsorbingresin in another cycle. The last eluate was fortified with S0 to bringit up to 60 g./1. and the pH adjusted to 1. It was then used to elute afresh batch of resin, the

' cycles being repeated.

Patented May 17, 1960 This fraction of i A second batch of the resin ofExample 1 having a V loading of 243 g./l. with 14 g./l. Fe was elutedwith 2 column volumes of an eluant as described in Example 1, thecontact time being 1 minute as before, and the pH maintained at .65. Aneluate was produced having a composition in g./l. V 0 91.9 and Fe 5.55.The eluate was set to vanadium recovery as described in Example 1 and asecond 2 column volumes of eluant was recycled through the resin asdescribed in Example 1 maintaining a pH of .55. The resulting eluatecontaining in g./l. 28.8 V 0 and 1.4 Fe. It was likewise oxidized torecover the vanadium. The last eluant which was again 2 column volumeswas recycled with an average contact time of about 8-10 minutes, pHbeing maintained at 1.5. After substantially all of the vanadium hadbeen eluted, an eluate was produced with 1.0 g./l. V 0 and negligibleFe. This eluate after fortification with S0 and pH adjustment was reusedwith a fresh batch of resin as described in Example 1.

Example 3 A resin as described in Examples 1 and 2 containing 135 g./l.V 0 and 4 g./l. Fe was eluted with 2 column volumes of eluant asdescribed in Examples 1 and 2, the contact time being substantially thesame, and the pH being maintained at 0.7. An eluate was producedcontaining in g./l. 65.7 V 0 and 2.05 Fe.

A second elution was effected with a contact time of 8-10 minutes and apH maintained at 1.5. An eluate was produced containing in g./l. 2.31 V0 and 0.1 Fe. After fortification with S0 and adjustment of pH this wasreused as an eluant for a fresh batch of resin as described in thepreceding examples.

In the examples the last elution has been described as a recycling witha relatively long retention time. Where the equipment makes itdesirable, it is possible to obtain substantially the same result byallowing the eluant simply to-remain in contact with the resin until theresin is substantially exhausted. This will usually require a time ofthe order of l-3 hours and is somewhat slower than the proceduredescribed in the example where the eluant is slowly recycled through theresin.

r 2,987,073 I I p i I claim: 1. A method of'eluting pentavalcnt vanadium-valu adsorbed on anion exchange resins which comprises eluting aportion of the vanadium values from the resin with a strongly acidaqueous sulfurous acid solution having a pH below 2, the rate of elutionbeing in excess of that at which any vanadium compound is precipitatedin the resin in unelutable form, such precipitation resulting from slowelution, adding sufiicient acid to the eluate to maintain the pH between1.3 and 2, maintaining elution at the above-defined rate until thevanadium radical content of the anion exchange resin is reduced to apoint at which the said slow elution does not precipitate a vanadiumcompound in unelutable form and recycling the eluate while maintainingthe pH between 1.3- and 2 until the vanadium radical content of theresin has been substantially eluted and recovering vanadium compoundsfrom the eluate by precipitation.

-2. The process of claim 1 in which the pH is adjusted during theelution by the addition of small amounts of sulfuric acid. 7

3. The process of claim 1 in which the recycled strongly acid aqueoussulfurous acid solution has a pH above 1.3 and below 2.

4. A process according to claim 1 in which the recycling with smallamount of eluant is maintained until the major proportion of thevanadium containing radical has been eluted to form a concentratedeluate and the elution is then completed with larger volumes of eluantto produce a relatively dilute eluate and the dilute eluate produced isused in the elution of fresh batches of resin after adjustment ofsulfurous acid content and of the pH to below 2.

References Cited in the file of this patent McLean et al. in U.S. AtomicEnergy Commission publication ACCO-63, July 30, 1954 (note especiallypages23, 28 and 48).

Abrams et al. in U.S. Atomic Energy Commission publication ACCO-53, July10, 1954.

Salmon et al.: Journal of the Chemical Society (1952), pages 2324-2326.

Sussman et al.: Industrial and Engineering Chemis- 7 try, vol. 37, No.7, pages 618-624..

1. A METHOD OF ELUTING PENTAVALENT VANADIUM VALUES ADSORBED ON ANIONEXCHANGE RESINS WHICH COMPRISES ELUTING A PORTION OF THE VANADIUM VALUESFROM THE RESIN WITH A STRONGLY SAID AQUEOUS SULFUROUS ACID SOLUTIONHAVING A PH BELOW 2, THE RATE OF ELUTION BEING IN EXCESS OF THAT ATWHICH ANY VANADIUM COMPOUND IS PRECIPITATED IN THE RESIN IN UNELUTABLEFORM, SUCH PRECIPITATION RESULTING FROM SLOW ELUTION, ADDING SUFFICIENTACID TO THE ELUATE TO MAINTAIN THE PH BETWEEN 1.3 AND 2, MAINTAININGELUTION AT THE ABOVE-DEFINED RATE UNTIL THE VANADIUM REDICAL CONTENT OFTHE ANION EXCHANGE RESIN IS REDUCED TO A POINT AT WHICH THE SAID SLOWELUTION DOES NOT PRECIPITATE A VANADIUM COMPOUND IN UNELUTABLE FORM ANDRECYCLING THE ELUATE WHILE MAINTAINING THE PH BETWEEN 1.3 AND 2 UNTILTHE VANADIUM RADICAL CONTENT OF THE RESIN HAS BEEN SUBSTANTIALLY ELUTEDAND RECOVERING VANADIUM COMPOUNDS FROM THE ELUATE BY PRECIPITATION.